The prior art describes numerous methods for quantitative determination of an analyte in a specified analysis sample. The various detection reactions are based on different principles. These include conversion of the analyte to be detected to a demonstrable substance, in which case, for instance, a coloured compound is produced and the degree of colouration is a measurement of the quantity of the analyte in question. Other detection methods are based on specific interactions between the analyte and a bonding partner. These include, for example, the detection method utilising the specific interaction between an antigen and an antibody, a ligand and its associated receptor or the hybridisation of complementary nucleic acid molecules. This type of detection method or assays are generally also described as affinity assays. With the affinity reactions on which they are based, there is generally the production of a stoichiometrically defined but not covalent complex formed from bonding partners specific to the analyte (e.g. a receptor, antibody) and the analyte (e.g. a ligand, antigen). Frequently, biomolecules like proteins take part in these reactions. But reactions can also exist between low-molecular substances, e.g. low-molecular receptor ligands, and a high-molecular substance, e.g. the receptor. A special variation of this affinity assay is based on immuno-assay in which the specific interaction between an antibody and an antigen is exploited. At the level of nucleic acid, a specific interaction can take place between two different nucleic acid molecules by means of mutually complementary sequential segments. By means of hybridisation of the complementary sequences, the formation of a double-stringed nucleic acid molecule results.
The assays cited are applied in numerous technical fields. These include clinical analysis/diagnostics, environmental analysis, genome analysis, active ingredient testing and even gene expression studies and gene bank screenings. Frequently several hundred samples are tested in parallel on a single sample carrier. This so-called “micro-array technique” nowadays achieves increased significance in so-called “high-throughput screenings”.
The advantage with assays based on affinity reactions when compared with assays based on chemical conversion of the analyte is that more elaborate preparation of the sample is generally not required. Separation of the analyte from undesirable impurities is rather accomplished by means of the specific interaction with a suitable bonding partner, the latter deliberately selecting, as it were, the analyte desired from the analysis sample.
Immuno-assays constitute a particularly widespread variant of affinity assays based on the specific interaction of antibodies and antigens. In the case of so-called ELISA (Enzyme Linked Immuno-Sorbent Assay), one of the reactants (i.e. either the analyte or the associate bonding partner) is in the sample carrier, frequently constituting a micro-titre plate, in immobilised form. In the course of the test, one or more components of the test system form a complex with the immobilised component. The quantity of the complex formed serves as a measurement of the concentration of the analyte in the sample. Two common variants of this test format are made up of the “sandwich assay” and the “competitive assay”. With the sandwich assay, for instance, the analyte is complexed by two further components (often two different antibodies) so that a ternary complex is generated on the sample carrier's surface. With the competitive assays, the analyte and a labelled component, frequently an analyte carrying a marker, compete f or a limited number of bonding positions.
A standard immuno-assay in heterogeneous phase frequently comprises the following processes:                Specification of a solid sample carrier;        Administration of analysis sample and a detection reagent;        Waiting for the binding equilibrium to set;        Rinsing out unbonded segments;        Measuring the bonded segments.        
Where applicable, these steps can be repeated several times with complex protocols. At the end of the entire process, detection of the entire material then occurs which has been bound to the sample carrier in the course of the procedure. For this, a colouring enzyme reaction, electrochemical luminescence, fluorescence, radioactivity, etc. can be used as a signalling transmitter.
Some assay formats work in homogeneous phase, such as, for instance, the FPIA fluorescence polarisation immuno-assay, but which are in many respects complex or less flexible in the way of modification than assays in heterogeneous phase.
Common to practically all assays cited is that prior to the measurement signal separation of unbonded label (activity, measurement signal) and bonded label must take place. This is generally achieved by having the sample carrier subjected to one or more washing actions prior to measurement (taking the measurement signal). These washing actions, absolutely required in the current prior art, however, entail disadvantages. With sample carriers allowing for numerous detection reactions in a small space, as happens for instance with micro-titre or nano-titre plates, there exists the problem of “transfer,” i.e. sample activity is transferred by washing from one sample volume to another one. A further disadvantage of the processes in which physical separation of unbonded and bonded label (or activity) occurs, consists of the fact that no time-staggered observation of the bonding process and hence no examination of the interaction or reaction kinetics is possible.
Besides the above cited washing for separation of bonded and unbonded activity, with assays using filter strips, separation takes place between unbonded activity and bonded activity by means of diffusion of the liquid phase in the porous solid phase formed by the filter. Assays of this type are usually set up for single samples.